First of all I'd like to mention that the syntax is secondary to the design of system. It is possible to express OO design using purely procedural syntax (case in point: first C++ compilers were actually just preprocessors which generated C code they feed to real C compilers). And of course it is quite possible to write purely procedural code using OO syntax.

The syntax meth($obj) will work as substitution for $obj->meth() until you need data abstraction (i.e. you don't have classes which share same interfaces, particulary your class tree is flat and you don't use inheritance). Some would argue that data abstraction is essential property of OO design and if a system doesn't use data abstraction it is not OO at all.